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z15 µarch
General Info
Arch Type	CPU
Designer	IBM
Manufacturer	GlobalFoundries
Introduction	September 12, 2019
Process	14 nm
Core Configs	12
Pipeline
Type	Superscalar, Pipelined
OoOE	Yes
Speculative	Yes
Reg Renaming	Yes
Instructions
ISA	z/Architecture
Cache
L1I Cache	128 KiB/core 8-way set associative
L1D Cache	128 KiB/core 8-way set associative
L3 Cache	256 MiB/chip 32-way set associative
L4 Cache	960 MiB/drawer 60-way set associative
Succession
z14

z15 is the successor to the z14, a 14 nm z/Architecture mainframe microarchitecture designed by IBM and introduced in 2019.

This article is a work in progress!

Process Technology

IBM fabricates its z15 microprocessors and system controllers on GlobalFoundries's 14 nm (14HP) FinFET Silicon-On-Insulator (SOI) process featuring highly-dense deep trench structures used for high-density eDRAM.

Release Dates

The z15 was launched by IBM on September 12, 2019. General availability of the z15 mainframe started September 23.

Architecture

Key changes from z14

• Higher scalability
  • Up to 190-way multiprocessing (from 170-way)
• Central Processor (CP)
  • 2 more cores (12, up from 10)
  • Core
    • 10-13% higher IPC (IBM claim)
    • Front-end
      • Improved branch predictor
        • New TAGE predictor
        • BTB pre-buffer (BTBp) replaced by a simpler write buffer
          • single double-bandwidth port (two independentread ports)
        • 2x larger L1 BTB (8 sets of 2K rows, up from 4 sets of 2K rows)
    • Back-end
      • Larger GCT (60 groups, up from 48 groups)
        • Wider retire (12 instructions/cycle, up from 10)
      • Larger Issue Queues (2 x 36-entry, up from 2 x 30-entry)
      • 2x larger mapper (128-entry, up from 64-entry)
      • Larger integer physical register files (???, up from 120 entries)
      • Larger vector physical register files (???, up from 127 entries)
    • Execution engine
      • New Modulo Arithmetic (MA) unit
    • Memory subsystem
      • 2x larger L2 instruction cache (4 MiB, up from 2 MiB)
  • Shared L3
    • 2x larger L3 (256 MiB, up from 128 MiB)
  • New integration
    • Nest Acceleration Unit (NXU)
• System Controller (SC)
  • 1.4x Larger L4 cache (960 MiB, up from 672 MiB)

Overview

This article is a work in progress!

Mainframe

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System

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Drawer

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Central Processor

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Core

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Die

Central Processor (CP) Chip

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Core

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System Controller (SC) Chip

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